The present invention relates to a flow-measuring system including a venturi and a movably mounted measuring element which is charged by the pressure differential across the venturi, with a counterforce acting against the deflection force generated by the pressure differential and the measuring element being stabilized in its zero position independently of these forces by a position dependent resetting force.
A flow measuring system of this type is disclosed in German Published Patent Application DE-AS No. 1,110,892. The measuring element is the armature of an electromagnet. It is guided by means of a bellows and a diaphragm whose resetting forces stabilize it in a zero position. If fluid flows and the armature is thus deflected from its zero position, a contact switches on the electromagnet. The resulting magnetic pulling force repeatedly opens the contact in rapid succession, with the average current developing with the aid of smoothing members holding the vibrating armature in equilibrium against the deflection force at the switching limits of the contact. A resonant core magnetic field gauge is installed in a measuring air gap of the electromagnet and emits a measuring signal at a frequency which is proportional to the field intensity. Since the field intensity is proportional to the square root of the magnetic force, the above-mentioned frequency constitutes an output value which is proportional to the flow rate.
Because of the use of a magnetic field measuring device, however, this known flow measuring system is very complicated and expensive. The continous vibratory movement of the measuring element as a result of the two-point regulation adversely influences measuring accuracy. Also, in many cases the display of the output signal which appears in the form of a frequency requires high component expenditures.